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Question

The number of atoms present in one mole of an element is equal to Avogadro number. Which of the following element contains the greatest number of atoms?

A
4g He
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B
0.40g Ca
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C
12g He
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D
46g Na
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Solution

The correct option is C 12g He
Calculating the number of moles of elements


No. of moles
=Given mass of a substanceMolar mass of a substance

A. 4 g He (Molar mass = 4 g mol1)
No. of moles =44= 1 mol

B. 46 g Na (Molar mass = 23 g mol1)
No. of moles =4623= 2 mol

C. 0.40 g Ca (Molar mass = 40 g mol1)
No. of moles =0.4040= 0.01 mol

D. 12 g He (Molar mass = 4 g mol1)
No. of moles =124= 3 mol

Calculating number of atoms of elements

Number of atoms present in one mole of element is equal to Avogadro's number.

Number of atoms in 1 mole
=6.022×1023 atoms

Number of atoms in an element
= no. of moles ×6.022×1023

A. No. of moles of He = 1 mol
No. of atoms of He =1×6.022×1023
=6.022×1023 atoms

B. No. of moles of Na = 2 mol
No. of atoms of Na =2×6.022×1023
=12.044×1023 atoms

C. No. of moles of Ca = 0.01 mol
No. of atoms of Ca =0.01×6.022×1023
=6.022×1023 atoms

D. No. of moles of He = 3 mol
No. of atoms of He =3×6.022×1023
=18.066×1023 atoms


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